The present invention relates to a grip head for stretching or straightening a flat or plate-like workpiece.
A standard grip head or plyer as described in German patent document 3,205,701 of H. Kutz has a row of one-piece plates extending parallel to each other and symmetrical to both sides of a normally horizontal symmetry plane. The plates are identical and are each formed with a forwardly open mouth or cutout into which the edge of a plate workpiece is inserted and where it is wedged in place against a pair of separate liner bars fitted to the opposite edges of the mouth. Rear ends of the plates are welded to a pair of rigidifying beams carried by a hydraulic structure that pulls the head back parallel to the plane to stretch and/or straighten the workpiece whose edge is wedged in the mouth.
This system is quite simple and relatively effective. The plates are extremely rigid in their planes and the liner bars transmit the forces tending to spread the mouth to all the plates. The central plates are extra thick to compensate for the forces concentrated there, in particular when a narrow workpiece is being clamped. Nonetheless the device is extremely bulky and very heavy.
Another system described in German patent 3,633,480 of K. Claasen sandwiches the mouth-forming plates between a pair of rigid beams extending parallel to the mouth and the stack of plates. Thus this plyer can grip a relatively narrow workpiece. It also is, however, very heavy and bulky. The plates are forged and massive and the external beams are normally cast and very heavy.
It is therefore an object of the present invention to provide an improved plate-stretching or -straightening grip head.
Another object is the provision of such an improved plate-stretching or -straightening grip head which overcomes the above-given disadvantages, that is which is extremely strong but that is still relatively compact.
A further object is to make such a grip head or plyer that can be assembled or serviced in the field.
A metal-stretching grip head has according to the invention a row of parallel upper plates wholly to one side of a plane and having front ends and rear ends and a row of parallel lower plates wholly to an opposite side of the plane and having front ends forming at the plane with the front ends of the upper plates a mouth slot extending along the plane and open forwardly on the plane. The lower plates also have rear ends juxtaposed across the plane with the upper-plate rear ends. A one-piece C-section metal bar is snugly received in the mouth slot. Rigid structure separate from the plates and bar fixes the plates relative to one another.
This sandwich construction makes it possible to assemble and service the unit in the field. In addition the C-section mouth bar is made of one piece, e.g. of forged steel, so it is very strong in and of itself, making the entire grip head very rigid. The plates themselves can be made of stiff but inexpensive sheet metal, making the assembly light and inexpensive at no reduction in strength.
The structure in accordance with the invention includes upper and lower rear beams engaging upper and lower edges of the upper and lower plates rearward of the mouth slot, and tie bolts extending across the plane between the rear beams. Spacers are provided between the beams. In addition a steel spacer box is provided between the upper and lower plates rearward of the mouth slot. The plane bisects the spacer box.
The head can also have upper and lower front beams engaging upper and lower edges of the upper and lower plates level with the mouth slot and tie bolts extending across the plane between the front beams.